U.S. Pat. No. 5,160,336 discloses an intracorporeal lithothripter having a handpiece which is adapted for holding a probe. The probe forms a waveguide which is adapted to transmit impact energy that is produced by a projectile. The projectile is pneumatically driven within a guide tube for periodically causing an impact force against the proximal end of the probe to thereby obtain shock waves at the distal end of the probe.
The efficiency of the probes as used with such lithotripters is dependent on the transfer of energy as well as also of the transformation of energy which is caused by the impact energy acting on the proximal end of the probe and being transmitted to its distal end as a shock wave resulting from such impact energy. The particular shock wave which is accordingly transmitted from a head portion to a tip portion of the probe may be considered as a repeating sequence of compressions and expansions whereby the propagation also results in a translational movement of the distal end of the probe which finally generates a deformation wave that causes the specific intracorporeal fragmentation of calculi. It is therefore to be understood that the geometric dimensions of the probe highly influence the propagation of the shock waves so that optimization of the geometric dimensions of the probe is considered as a very essential object in particular for use in a lithotripter operating with ultrasonic frequencies of the shock waves for obtaining a particle size of the calculi as fragmented by such a probe which for example may be flushed via a separate flush channel of the endoscope into which the probe has been inserted by the operator of the lithotripter.
The metallic probes which so far have been used in lithotripsy in combination with an intracorporeal lithotripter of the kind as mentioned above are usually provided with a uniform diameter of between 0.6 mm as a minimum and 3.2 mm as a maximum with an average length of the probe of about 500 mm. The probes having the smaller diameter may also be used with so-called flexible endoscopes which could also be provided with a controllable tip portion. The same mostly necessitates larger operation lengths of the probe of up to 700 mm and more for allowing a deflection of such flexible endoscopes in two directions with a circular measure by radians of up to 170.degree.. For obtaining with such a large deflection of the endoscope a correspondingly high flexibility of the probe it already has been suggested in U.S. Pat. No. 5,449,363 to provide the probe with a flattening over the actual partial length which has to take up the deflection of the endoscope whereby the provision of such a flattening is at the same time intended to avoid any unwanted frictional contact with the surrounding wall of the lumen of the endoscope. It is further disclosed in this document that such a flattening could also allow a laser cutting or electrical discharge machining of slits at selected locations to further improve flexibility of the probe.
As the result of the relatively high stress and loading to which the head portion of the probes is exposed by the impact force as continuously produced by the pneumatically driven projectile there actually exists an enlarged risk of fractures at arbitrary portions along the length of the probe. Such fractures of the probe could lead to injuries of the patient in the course of an endoscopic treatment and could also result in damages of the wall of the working channel of the endoscope. The presence of such fractures when not timely noticed could as well tempt the operator to continue with the endoscopic treatment then even with a defective probe which would make the operation imperfect and possibly also incomplete.